Heavy duty engines, and particularly diesel engines of the reciprocating type having poppet valves, utilize an articulated valve train to actuate such valves. Because of the duty cycle usually experienced by this type of engine, substantial components must be used in the valve train. In addition, such engines may also include a cam actuated fuel injection system to achieve ultra high injection pressures when the engine has a unit injector fuel system. For such engines it is not enough to have a hydraulic lifter system similar to those found in automotive applications.
Consequently the clearance between the articulated joints in the valve train must be set within close tolerances to accommodate thermal expansion when an engine is fully heated up, while at the same time providing adequate lift to open valves fully and to displace fuel injector plungers generating sufficient pressure for a fuel injection system. Many systems have been developed to set the lash, particularly in the case of what is referred to as a rocker arm actuating overhead valves. Such rocker arms usually have a threaded component at one end of the rocker arm to displace a contact surface to achieve the necessary clearance between adjacent components, such as the rocker arm and a pushrod. When an engine is in the field, it is periodically necessary to reset the lash to accommodate expected wear in the valve train of an engine. This is done by hand, which is unsuitable for high volume engine production.
A number of systems have been proposed for automating the valve lash adjustment on a production volume basis. These involve automated devices for turning the threaded elements to the point where they achieve the necessary clearances within production tolerances. With any such system there needs to be a check or verification on a statistical basis that the automated system is, in fact, providing the correct lash adjustment. This is generally done using individual instruments. However, when the valve rocker arm has additional elements to provide adjacent component abutting surfaces, the rocker arm has uneven surfaces that are unsuitable for measuring such lash.
Accordingly, there exists a need in the art for accurately determining the lash of a valve train in such an environment.